The present invention relates to a process for manufacturing expanded grain products without extended time or high energy requirements. More specifically, the present invention is directed to a low moisture hot rolling process for preparing expanded grain products.
Processes to make expanded grain products can be divided into three categories: extrusion, sudden pressure drop and oven puffing or toasting processes. The extrusion process involves feeding a mixture of moistened grain flour, flavorings and colorings into a cooker extruder. The mixture is thoroughly cooked into a plastic mass which expands when exiting the die. The cooking temperature can be adjusted so that the extrudate exits the die as a translucent dense glass which will expand when heated in hot oil or hot air. The process requires a high capital investment and is energy intensive.
The sudden pressure drop process involves heating the grain in a closed chamber to the desired temperature then rapidly releasing the pressure which has built up inside the chamber. This process can be modified so that the grain is heated in an open chamber then transferred to a closed chamber prior to applying a vacuum to induce expansion. This type of process requires a high capital investment for special equipment and is very expensive to operate.
The present invention belongs to the oven puffing or toasting category. The oven puffing process can be subdivided into two groups: those with and those without bumping treatment. Bumping is a process whereby the grain or kernel thickness is reduced by some physical means, e.g. compression. Examples of preparing rice products with no bumping treatment are clearly shown in U.S. Pat. Nos. 2,715,579; 2,610,124; 2,808,333; and 3,085,013. These processes employ various methods to heat the parboiled grain or pregelatinized grain to induce a low degree of expansion.
In most of the prior art processes that employ a bumping step, the grain is steamed in a rotary cooker to gelatinize the starch and increase the grain moisture content. The cooked grain is then rolled with or without a partial drying step, and then the bumped grain is dried at a fairly low temperature to reduce the moisture content of the grain to about 11%-15% moisture. The dried grain is then tempered for no less than 15 hours prior to puffing in the oven or a stream of hot air.
Australian Patent International Publication Number WO 86/05953, describes a process which involves wetting the parboiled grain with a solution containing a diastase(s) and/or a proteolytic enzyme(s), salt or sugar. The moistened grain was held at temperatures below the starch gelatinization temperature to allow uniform redistribution of the added water. The tempered grain (23% moisture) was bumped and dried to 12%-15% moisture. The partially dried grain was allowed to rest and then toasted in the oven. Examples given in the patent used several days of rest time. The authors claimed that tempering and bumping the grain at temperatures below the starch gelatinization temperature plus the use of enzyme(s) produce crisped grain with superior quality.
The present invention involves wetting the parboiled grain preferably to a moisture content of about 8%-16% using a solution containing salts e.g. phosphates, citrates, chlorides, sulfates and the like, and sugars e.g. corn syrups, sucrose and the like. The moistened grain is then tempered. Tempering is a process whereby uniform distribution of moisture throughout the grain is achieved. The required tempering time is a function of tempering temperature.
Satisfactory crisped rice can be obtained using about 20 minutes tempering at about 50.degree. C. The tempered rice is plasticized using heat then bumped to reduce the kernel thickness. The heating has to be carried out in a short time to minimize moisture loss. The desired temperature for rolling is inversely proportional to the rice moisture content. The bumped grain can be toasted with or without resting to obtain expanded products.